Control of abdominal extension in the freely moving intact crayfish Cheraxdestructor - I. Activity of the tonic stretch receptor

Electrical recordings were made from the sensory neurone of the tonic muscl e receptor organ in the abdomen of the intact, freely behaving crayfish Che rax destructor. Slow extensions of the abdomen were evoked by lowering a pl atform from beneath the suspended crayfish, and the movements and tonic sen sory neurone activity were video-recorded simultaneously. The recordings sh owed that the tonic sensory neurone was active when the abdomen was fully f lexed prior to the extension. When the extension began, however, the sensor y neurone ceased firing shortly after movement was detected, irrespective o f the load applied to the abdomen. When the abdomen was physically blocked from extending fully, the sensory neurone did not fire. The tonic muscle re ceptor organ is considered to be the length-detecting sensor for a load-com pensating servo-loop, but the results demonstrate that its activity pattern during extensions evoked by a platform-drop in C. destructor are not consi stent with that role.